This invention relates to a sewer system.
There are three basic types of known sewer systems. The most frequently used is the conventional gravitation sewer system having sewer pipes inclined downwards, in which the waste water flows by gravitation. In the pressure sewer system overpressure is used for transporting waste water through small-bore sewer pipes. The pressure system is not widely used, although it provides advantages such as small pipe dimensions and the possibility to lay pipes extending upward. In the vacuum sewer system, the pressure in the sewer pipe is reduced to about one half of atmospheric pressure and the pressure difference between the atmosphere and the reduced pressure in the sewer pipe is used for the transportation of sewage. The vacuum sewer system has achieved wide use in ships, aircraft and trains. In principal, it has the same advantages as the pressure sewer system. The main disadvantages of the vacuum sewer system are a relatively high cost and the fact that the sanitary units connected to the sewer must be separated from the sewer system by a normally closed discharge valve, which may cause flooding problems.
A fourth type of known sewer system is the low vacuum sewer system. The low vacuum sewer system is technically between the gravitation sewer system and the vacuum sewer system. In the case of the low vacuum sewer system, the toilet bowl may be connected to the sewer pipe through a trap, as in a gravity sewer system, or through a normally-closed discharge valve, as in the normal vacuum sewer system. For emptying a toilet bowl of a low vacuum system, a relatively low vacuum (about 0.1 to 0.4 bar below atmospheric) is generated in the sewer pipe. In some known systems of this type, a sluice device has been used as an interface between the space that is under vacuum, such as the sewer pipe, and a collecting container under atmospheric pressure. Such sluice devices have poor operational reliability because of leakage caused by deposits on the sealing surfaces of the sluice. Patent Publication SE 358196 describes a low vacuum system where the generation of vacuum requires a check valve in the sewer pipe. Practice has shown that such a check valve will not function satisfactorily in the long run. Furthermore, it is difficult to avoid dirt being drawn into the ducts that lead from the sewer pipe to the vacuum generator and which should normally contain only air. These difficulties seem to have been detrimental for marketing devices according to Patent Publication SE 358196. In general, known systems of this kind have had such a primitive or crude design that their operational reliability has suffered. They have been marketed substantially only as individual toilet units for summer cottages or the like.